The category of number is based on a two-member opposition: singular vs. plural. An interesting feature of this category is the fact that it is blended with person: number and person make use of the same morpheme. As person is a feature of the present tense, number is also restricted to the present tense.
The analysis of the examples demonstrates the weakness of the English verb as concerns the expression of person and number and its heavy reliance on the subject: it is the subject that is generally responsible for the expression of person and number in English.